The present invention generally relates to a unit belonging to a network of units coupled together through transmission lines like cables (in this specification, such a unit will be called a xe2x80x9cnetwork unitxe2x80x9d). More particularly, the present invention relates to an improved power-saving network unit that can transition either manually or automatically from a normal mode into a power-saving mode, in which the overall power consumption of the unit can be reduced.
In a conventional network of this type, each power-saving network unit enters a power-saving mode if the unit has not been accessed by, or has been disconnected from, other units for a predetermined time or more, as in IEEE 1394 standards or Japanese Laid-Open Publication No. 7-134628. Once the power-saving network unit has entered the power-saving mode (i.e., a sleep mode), the unit cannot perform its normal operation until the modes are switched again. Therefore, exchange of data through the built-in ports thereof connected to the transmission lines is also suspended for a while.
When another power-saving network unit demands access to the power-saving network unit that has entered the power-saving mode, the latter unit can readily transition back into the normal operation mode as disclosed in Japanese Laid-Open Publication No. 7-93061, for example.
In the conventional power-saving unit network, where a unit is connected to the other units through transmission lines, if the former unit has not been accessed by any other unit for a predetermined period or the number of times the unit in question has been accessed by other units during the period (in this specification, this number of times will be called a xe2x80x9cfrequency of accessesxe2x80x9d) is a preset one or less, then the unit enters the power-saving mode. Accordingly, even if the network unit in question is a relay node located between a pair of other network units, the former unit still enters the power-saving mode. Suppose data should be exchanged between the pair of network units by way of the network unit in the power-saving mode. First, the ports of the network unit in the power-saving mode should be enabled such that data can be exchanged therethrough. Then, the data should be transmitted from one of the pair of network units to the other through the network unit in the power-saving mode. Thus, in such a situation where data should be exchanged between a pair of normally operating network units via a network unit in the power-saving mode, it takes an additional time to exchange the data. In other words, the data exchange is delayed for the time needed to enable the ports of the network unit in the power-saving mode.
An object of the present invention is providing a power-saving network unit that can fulfill the requirements of high-speed operation and reduced power consumption at the same time. Specifically, if any network unit is needed for a pair of other network units to exchange data therethrough (e.g., if the former unit is a relay node therebetween), then the former unit is prohibited from entering the power-saving mode such that the data can be exchanged quickly.
To achieve this object, according to the present invention, it is determined whether or not each of power-saving units, which a network is made up of, may enter the power-saving mode by examining interconnection relationship among these power-saving units.
Specifically, a power-saving network unit according to the present invention is connected to a network made up of a plurality of units that are coupled together through transmission lines and is operative in either normal operation or power-saving mode. The power-saving network unit includes: information storage means for storing information representing a configuration of the network; and power-saving mode setting means for determining, based on the network configuration information stored on the storage means, whether or not the power-saving network unit may enter the power-saving mode.
In one embodiment of the present invention, the power-saving network unit may further include: peripheral I/O means connected to the network; and digital processing means for receiving information from other units in the network and processing the information. If the mode setting means has determined that the power-saving network unit may enter the power-saving mode, the peripheral I/O and digital processing means preferably receive an instruction signal from the mode setting means to enter the power-saving mode.
In another embodiment, if the power-saving network unit is master of the other units in the network, then the mode setting means preferably prohibits the power-saving network unit from entering the power-saving mode.
In still another embodiment, if the power-saving network unit is a relay node located between a pair of other units in the network, then the mode setting means preferably prohibits the power-saving network unit from entering the power-saving mode.
In yet another embodiment, if the power-saving network unit is neither master nor relay node in the network, then the mode setting means preferably removes prohibition against the power-saving network unit""s entering the power-saving mode.
In yet another embodiment, the power-saving network unit may further include counting/comparing means for counting and/or comparing a frequency with which the power-saving network unit has been accessed by other units in the network. If the power-saving network unit is neither master nor relay node in the network, then the mode setting means preferably allows the power-saving network unit to enter the power-saving mode based on the frequency counted and/or compared by the counting/comparing means.
In still another embodiment, the power-saving network unit may further include switch means turning ON responsive to human manipulation or a human being absence signal supplied from a human being sensor. The switch means is preferably connected to the counting/comparing means. When the counting/comparing means receives an ON signal from the switch means, the counting/comparing means compulsorily outputs a signal indicating that the frequency of accesses is a reference value or less.
In still another embodiment, the power-saving network unit may further include means for deciding whether or not the power-saving network unit is connected to the network. An output of the deciding means is preferably input to the storage means, and the network configuration information that has been stored on the storage means is preferably modified based on a result of decision made by the deciding means.
In still another embodiment, the power-saving network unit may further include means for monitoring and revising the configuration of the network at regular intervals. An output of the monitoring means is preferably input to the storage means, and the network configuration information that has been stored on the storage means is preferably modified based on the network configuration revised by the monitoring means.
In still another embodiment, each of the peripheral I/O and digital processing means is preferably divided into: a circuit section needed in relaying information from the other units connected to the network; and the other circuit sections only the circuit sections, other than the circuit section needed in relaying the information, of the peripheral I/O and digital processing means are preferably allowed to enter the power-saving mode.
According to the present invention, it is determined based on the configuration of a network whether or not a power-saving network unit may enter a power-saving mode. For example, if the power-saving network unit is master of the other units or a relay node located between a pair of other units in the network, then the power-saving network unit is prohibited from entering the power-saving mode, and is locked to the normal operation mode. The conventional power-saving network unit always enters the power-saving mode no matter whether the unit is a relay node or not. Thus, according to the conventional power conservation techniques, it is necessary to get the network unit ready for data exchange by making the unit transition back into the normal operation mode. In contrast, since such a mode transition is not required by the present invention, data can be exchanged faster than the conventional network.
In particular, according to the present invention, if the power-saving network unit has been disconnected from, or subsequently reconnected to, the network, then such disconnection or reconnection is recognized by the deciding means. Based on the information recognized, the network configuration information stored on the storage means is modified. Thus, it is possible to appropriately get the power-saving network unit switched into the power-saving mode or locked to the normal operation mode.
Also, according to the present invention, even if the network configuration has been changed, the monitoring means monitor the network configuration and feeds a revised network configuration back to the storage means at regular intervals. Thus, no matter whether the network configuration is changed or not after that, all the power-saving network units can be appropriately switched into the power-saving mode or locked to the normal operation mode.
Furthermore, according to the present invention, if the power-saving network unit is required just for the information relay purposes, then only the circuit section thereof needed in relaying information may be locked to the normal operation mode, while the other circuit sections may enter the power-saving mode. Thus, the power can be further saved.